1. Field of the Invention
Embodiments of the invention relate to the field of software, and more specifically, to program transformation.
2. Description of Related Art
Modern network processors generally have asynchronous, or non-blocking, memory access operations, so that other computation work may be overlapped with the latency of the memory accesses. For instance, every memory access instruction is non-blocking and is associated with an event signal. That is, when a memory access instruction is issued, other instructions following it may continue to run while the memory access is in flight, until a wait instruction for the associated signal blocks the execution. Once the memory access is completed (e.g., its result is available), the associated signal is asserted by the hardware and the wait instruction then clears the signal and returns to execution. Consequently, all the instructions between the memory access instruction and the wait instruction may be overlapped with the latency of the memory access. In addition, modern network processors usually have a highly parallel architecture and are multi-threaded. For example, whenever a new packet arrives, a series of tasks (e.g., receipt of the packet, routing table look-up, and en-queuing) is performed on that packet by a new thread. In such a parallel programming paradigm, accesses to global resources (e.g., memory) are protected by critical sections to ensure the mutual exclusiveness and synchronizations between threads
Together with the asynchronous memory access operations, the multi-threading/multi-processing programming model helps hide the long memory access latency, by overlapping the latency of the memory access in one thread with the latency of memory accesses and/or the computations in other threads. However, if both the memory access and its associated wait instruction are contained in the same critical section, the memory latency hiding is greatly impacted due to the sequential execution of the critical section between threads. This may result in performance degradation.